1. Technical Field
The invention relates to a method for image correction and an image projection apparatus using the same. More particularly, the invention relates to a method for correcting the geometric distortion of an image and an image projection apparatus using the same.
2. Related Art
Microelectromechanical systems (MEMS) refer to a research area utilizing microelectronic and micromechanical techniques to manufacture or develop related electronic devices and mechanical structures to microminiaturize related products. Due to its technical effects such as small size and low power consumption, an image projection apparatus employing a MEMS scanning device may be applied in handheld electronic products (e.g. smartphones or notebook computers) to enhance the usage convenience of the image projection apparatus, and to replace the traditional desk type or fixed image projection apparatuses.
Typically speaking, the image projection apparatus utilizing the MEMS scanning device employs a projection light source to provide a projection light beam. Moreover, the projection light beam is projected on a projection plane by using optical elements such as the MEMS scanning device and reflection mirrors. An image is formed by oscillating the scanning mirror inside the MEMS scanning device on the fast and slow axes to move the projection light beam to scan on the projection plane, as well as by the human visual retention characteristics. When operating the MEMS scanning device, typically different respective control signals are used to control oscillation frequency and angle of the scanning mirror on the corresponding axial direction (e.g. fast and slow axes), so as to control the scanning speed and direction of the projection light beam on the projection plane. However, in the process of moving the projection light beam to scan and project to the projection plane, due to the planarity of the reflection plane of the scanning mirror and/or the optical path problems such as refraction and reflection caused by the optical elements, the projection path of the projection light beam may change. Accordingly, the projection image may be geometrically distorted, thereby affecting the image display quality. Moreover, since the oscillation of the MEMS scanning device on the fast axis is typically controlled by a periodic sine wave, therefore, when the MEMS scanning device moves the projection light beam to project near a projection boundary and is about to reverse scan direction, the oscillation speed of the MEMS scanning device comparatively decreases and generates issues such as uneven scanning speed for the projection light beam.
Conventional techniques typically correct for the geometric distortion of the projection image with lens configurations. However, configuring lenses may lower the light efficiency of the projection light beam and correspondingly increase the manufacturing costs of the image projection apparatus. Therefore, researchers are looking for direct and simple methods to correct the geometric distortion of projection images.